/*
Copyright 2018 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package storage

import (
	"context"
	"fmt"
	"time"

	authenticationapiv1 "k8s.io/api/authentication/v1"
	"k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/util/validation/field"
	"k8s.io/apiserver/pkg/authentication/authenticator"
	genericapirequest "k8s.io/apiserver/pkg/endpoints/request"
	"k8s.io/apiserver/pkg/registry/rest"
	"k8s.io/apiserver/pkg/warning"
	authenticationapi "k8s.io/kubernetes/pkg/apis/authentication"
	authenticationvalidation "k8s.io/kubernetes/pkg/apis/authentication/validation"
	api "k8s.io/kubernetes/pkg/apis/core"
	token "k8s.io/kubernetes/pkg/serviceaccount"
)

func (r *TokenREST) New() runtime.Object {
	return &authenticationapi.TokenRequest{}
}

// Destroy cleans up resources on shutdown.
func (r *TokenREST) Destroy() {
	// Given no underlying store, we don't destroy anything
	// here explicitly.
}

type TokenREST struct {
	svcaccts             rest.Getter
	pods                 rest.Getter
	secrets              rest.Getter
	issuer               token.TokenGenerator
	auds                 authenticator.Audiences
	audsSet              sets.String
	maxExpirationSeconds int64
	extendExpiration     bool
}

var _ = rest.NamedCreater(&TokenREST{})
var _ = rest.GroupVersionKindProvider(&TokenREST{})

var gvk = schema.GroupVersionKind{
	Group:   authenticationapiv1.SchemeGroupVersion.Group,
	Version: authenticationapiv1.SchemeGroupVersion.Version,
	Kind:    "TokenRequest",
}

func (r *TokenREST) Create(ctx context.Context, name string, obj runtime.Object, createValidation rest.ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error) {
	req := obj.(*authenticationapi.TokenRequest)

	// Get the namespace from the context (populated from the URL).
	namespace, ok := genericapirequest.NamespaceFrom(ctx)
	if !ok {
		return nil, errors.NewBadRequest("namespace is required")
	}

	// require name/namespace in the body to match URL if specified
	if len(req.Name) > 0 && req.Name != name {
		errs := field.ErrorList{field.Invalid(field.NewPath("metadata").Child("name"), req.Name, "must match the service account name if specified")}
		return nil, errors.NewInvalid(gvk.GroupKind(), name, errs)
	}
	if len(req.Namespace) > 0 && req.Namespace != namespace {
		errs := field.ErrorList{field.Invalid(field.NewPath("metadata").Child("namespace"), req.Namespace, "must match the service account namespace if specified")}
		return nil, errors.NewInvalid(gvk.GroupKind(), name, errs)
	}

	// Lookup service account
	svcacctObj, err := r.svcaccts.Get(ctx, name, &metav1.GetOptions{})
	if err != nil {
		return nil, err
	}
	svcacct := svcacctObj.(*api.ServiceAccount)

	// Default unset spec audiences to API server audiences based on server config
	if len(req.Spec.Audiences) == 0 {
		req.Spec.Audiences = r.auds
	}
	// Populate metadata fields if not set
	if len(req.Name) == 0 {
		req.Name = svcacct.Name
	}
	if len(req.Namespace) == 0 {
		req.Namespace = svcacct.Namespace
	}

	// Save current time before building the token, to make sure the expiration
	// returned in TokenRequestStatus would be <= the exp field in token.
	nowTime := time.Now()
	req.CreationTimestamp = metav1.NewTime(nowTime)

	// Clear status
	req.Status = authenticationapi.TokenRequestStatus{}

	// call static validation, then validating admission
	if errs := authenticationvalidation.ValidateTokenRequest(req); len(errs) != 0 {
		return nil, errors.NewInvalid(gvk.GroupKind(), "", errs)
	}
	if createValidation != nil {
		if err := createValidation(ctx, obj.DeepCopyObject()); err != nil {
			return nil, err
		}
	}

	var (
		pod    *api.Pod
		secret *api.Secret
	)

	if ref := req.Spec.BoundObjectRef; ref != nil {
		var uid types.UID

		gvk := schema.FromAPIVersionAndKind(ref.APIVersion, ref.Kind)
		switch {
		case gvk.Group == "" && gvk.Kind == "Pod":
			newCtx := newContext(ctx, "pods", ref.Name, gvk)
			podObj, err := r.pods.Get(newCtx, ref.Name, &metav1.GetOptions{})
			if err != nil {
				return nil, err
			}
			pod = podObj.(*api.Pod)
			if name != pod.Spec.ServiceAccountName {
				return nil, errors.NewBadRequest(fmt.Sprintf("cannot bind token for serviceaccount %q to pod running with different serviceaccount name.", name))
			}
			uid = pod.UID
		case gvk.Group == "" && gvk.Kind == "Secret":
			newCtx := newContext(ctx, "secrets", ref.Name, gvk)
			secretObj, err := r.secrets.Get(newCtx, ref.Name, &metav1.GetOptions{})
			if err != nil {
				return nil, err
			}
			secret = secretObj.(*api.Secret)
			uid = secret.UID
		default:
			return nil, errors.NewBadRequest(fmt.Sprintf("cannot bind token to object of type %s", gvk.String()))
		}
		if ref.UID != "" && uid != ref.UID {
			return nil, errors.NewConflict(schema.GroupResource{Group: gvk.Group, Resource: gvk.Kind}, ref.Name, fmt.Errorf("the UID in the bound object reference (%s) does not match the UID in record. The object might have been deleted and then recreated", ref.UID))
		}
	}

	if r.maxExpirationSeconds > 0 && req.Spec.ExpirationSeconds > r.maxExpirationSeconds {
		//only positive value is valid
		warning.AddWarning(ctx, "", fmt.Sprintf("requested expiration of %d seconds shortened to %d seconds", req.Spec.ExpirationSeconds, r.maxExpirationSeconds))
		req.Spec.ExpirationSeconds = r.maxExpirationSeconds
	}

	// Tweak expiration for safe transition of projected service account token.
	// Warn (instead of fail) after requested expiration time.
	// Fail after hard-coded extended expiration time.
	// Only perform the extension when token is pod-bound.
	var warnAfter int64
	exp := req.Spec.ExpirationSeconds
	if r.extendExpiration && pod != nil && req.Spec.ExpirationSeconds == token.WarnOnlyBoundTokenExpirationSeconds && r.isKubeAudiences(req.Spec.Audiences) {
		warnAfter = exp
		exp = token.ExpirationExtensionSeconds
	}

	sc, pc := token.Claims(*svcacct, pod, secret, exp, warnAfter, req.Spec.Audiences)
	tokdata, err := r.issuer.GenerateToken(sc, pc)
	if err != nil {
		return nil, fmt.Errorf("failed to generate token: %v", err)
	}

	// populate status
	out := req.DeepCopy()
	out.Status = authenticationapi.TokenRequestStatus{
		Token:               tokdata,
		ExpirationTimestamp: metav1.Time{Time: nowTime.Add(time.Duration(out.Spec.ExpirationSeconds) * time.Second)},
	}
	return out, nil
}

func (r *TokenREST) GroupVersionKind(schema.GroupVersion) schema.GroupVersionKind {
	return gvk
}

// newContext return a copy of ctx in which new RequestInfo is set
func newContext(ctx context.Context, resource, name string, gvk schema.GroupVersionKind) context.Context {
	oldInfo, found := genericapirequest.RequestInfoFrom(ctx)
	if !found {
		return ctx
	}
	newInfo := genericapirequest.RequestInfo{
		IsResourceRequest: true,
		Verb:              "get",
		Namespace:         oldInfo.Namespace,
		Resource:          resource,
		Name:              name,
		Parts:             []string{resource, name},
		APIGroup:          gvk.Group,
		APIVersion:        gvk.Version,
	}
	return genericapirequest.WithRequestInfo(ctx, &newInfo)
}

// isKubeAudiences returns true if the tokenaudiences is a strict subset of apiserver audiences.
func (r *TokenREST) isKubeAudiences(tokenAudience []string) bool {
	// tokenAudiences must be a strict subset of apiserver audiences
	return r.audsSet.HasAll(tokenAudience...)
}
